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Old aerial photos supply new knowledge on glaciers in Greenland

CLIMATE

The glaciers in southeast Greenland are retreating rapidly with the ongoing global climate change. But now research from the University of Copenhagen shows that the glaciers can recuperate within a short timeframe if temperatures are to drop. The results are based on a collection of Danish aerial photos combined with both old and modern satellite imagery as well as field work. The scientific results have created international attention and have been published as a cover story in the highly esteemed journal Nature Geoscience.

"We have managed to get an overview of the glacial evolution over a period of 80 years. This is the first time ever this has been done in a study of glaciers in Greenland. Results show that glaciers can recuperate within a short time frame if climate changes and temperatures drop, as it has in a period after the 1940s," says PhD student and lead-author on the project Anders Bjørk, from Professor Eske Willerslev's Centre for GeoGenetics from University of Copenhagen.

Anders Bjørk adds:

"Most of the scientific foundation, models, and theories on glaciers in Greenland and how global warming affects them are based on observations from satellites over the last ten years. Otherwise scientists have had to use previous warming events way into the past when wanting to compare today's massive retreat."

A fight for land between Denmark and Norway

The Danish explorer Knud Rasmussen and his seventh Thule-expedition in 1932-33 is a significant cause for the recent publication from Anders Bjørk and Dr. Kurt H. Kjær from the Natural History Museum of Denmark, University of Copenhagen. Results have created international attention as Greenland stands as an important region for northern latitudes are affecting the rest of the earth’s climate – including changes in glacial conditions and related sea-level rise.

Originally the many aerial photos, which have been achieved Danish National Survey and Cadastre, were used for producing new maps of the region in the early 1930s, as Denmark and Norway were fighting over the right of disposal of East Greenland, a fight without casualties which Denmark won at the International Court in Haag in the Netherlands in 1933.

Photos get a renaissanse

With help from the scientists and the Danish National Survey and Cadastre, the unique aerial photos have now gained a renaissance in a different setting where climate change and theories as “The Tipping Point” – where nature reaches a point where changes cannot be reversed are discussed.

"We have investigated no less than 132 glaciers on a 600 km coastal stretch in Southeast Greenland, both those who terminate on land and those who calve in the ocean. The historical photos have proven to be extremely valuable, and with these photos and other aerial photos recorded later during WWII and satellite imagery we are able to observe glacier change in very long historical context. In the early 1920s and 1930s, temperatures were high, similar to that of the present, and this affected the glacial melt. At the time many glaciers underwent a melt similar or even higher than what we have seen in the last ten years. When it became colder again in the 1950s and 1960s, glaciers actually started growing," says Dr. Kurt H. Kjær and underlines:

"There should be no doubt that if the current temperature rise in Greenland continues then we will have problems with the melting of the glaciers. We are already seeing it now on the marine terminating glaciers where changes in temperature and ocean currents are influencing their stability. Another remarkable discovery we did was that the observed changes are not just local, it is happening in the entire region," says Dr. Kjær.

Kurt H. Kjær has previously worked with his colleague Svend Funder from Center for GeoGenetics on investigating sea ice extent in the Arctic Ocean. Results showed that the sea ice extent has been far from stable throughout the last 10,000 years.